Aldora Tanks

[djanni]

I've never been diving with a steel tank for the simple reason that an AL80 will give me over an hour UW on a typical 80' dive with an ascending profile. I'll usually run out of bottom time before I'll run out of air and I'm 5'8 200 lbs. From what I've read a steel 100 really adds weight at the end of a dive as an AL80 at the end of a dive is + boyant while a steel 100 is- boyant by about 6 lbs. I've also read that a steel 100 only really gives you 100CF if it has been filled to its true full operating pressure which is higher than 3000PSI. If you get a 100CF steel tank filled to the standard 3000PSI which most do you're not getting 100CF. I hope some others here can add some more commentary as I kind of view the steel tanks for those who just like breathing more air or perhaps being more energetic under water. I always try to sip air and conserve energy UW.

Trip after trip, Aldora's tanks come in consistantly close to the STANDARD, 3,442psi. Aldora fills their own tanks. I understand that is the tanks rated pressure. We haven't had a fill as low as 3,300 is a really long time and we dive twice a week.

 

[BRT]

For some reason, this is a very difficult concept for people to understand. I remember teaching a DM class where all the students were baffled about the differences in tank capacities and pressures.

I don't consider myself a tank guru, but uncfnp is correct. A tank has the amount of gas advertised when it is filled to its rated pressure. If an HP 100's rated pressure is 3500 PSI, it will have 100 cubic feet when it is filled to 3500 PSI. If an AL 100 has a rated pressure of 3300, it will have 100 cubic feet when filled to 3300 PSI.

Where people get confused is when dissimilar tanks are filled to the same pressure. Let's say you have three tanks, all the same advertised capacity (100 cubic feet), and all filled to 3000 PSI. The LP tank (rated at 2640) will have the most, well over 100 cubic feet, because it has been filled over 10% more than its rated capacity. The AL tank (rated at 3300) is filled at about 10% less than its rated capacity, so it has a lot less. The HP tank (rated at 3500) will have the least, because it is filled to about 15% below its capacity.

None of this changes the fact that a "full" 3000# AL80 is only about 77 cubic feet. Some full HP steels are over their ratings.

 

[boulderjohn]

None of this changes the fact that a "full" 3000# AL80 is only about 77 cubic feet. Some full HP steels are over their ratings.

77.4, actually. Correct--not all tanks are exactly what they say they are. And the point is....?

 

[BRT]

77.4, actually. Correct--not all tanks are exactly what they say they are. And the point is....?

A tank does not necessarily have the advertised amount of air when filled too the rated pressure.

 

[Zman96]

Z man, that's a bit of a dangerous situation? no? what would you do if you had a failure of your BCD? Just asking.

That is why I don't dive 120s with my backplate, I would use my vest style BCD if I were going to. If I were using it I could easily kick upwards if needed with no air in it, for good trim along the bottom I would require air to keep me from damaging the reef.

 

[cvchief]

Not if they are both filled to their normal working pressure. 100cf is 100cf no matter where it comes from.

And therein lies the Cozumel issue. The 100 CF AL tanks in Coz are always short filled to 3000PSI, not 3300 as they should be.

 

[ggunn]

An HP steel 100 holds more gas than an AL 100, not because it's steel, but because it has a higher operating pressure. Sorry for the confusion.

What you are not considering is the difference in "dead" volumes (the volume of water a tank would hold) of the cylinders. An AL 100 holds 100cf at its operating pressure, as does a steel 100, and 100cf is 100cf. A steel 100 has a lower dead volume because of its higher pressure rating.

 

[djanni]

What you are not considering is the difference in "dead" volumes (the volume of water a tank would hold) of the cylinders. An AL 100 holds 100cf at its operating pressure, as does a steel 100, and 100cf is 100cf. A steel 100 has a lower dead volume because of its higher pressure rating.

Which form of "dead" volume are you referring to?

 

[Scubagolf]

And therein lies the Cozumel issue. The 100 CF AL tanks in Coz are always short filled to 3000PSI, not 3300 as they should be.

Why is this? Is it because the central station hot fills to 3300 and by the time the tanks are used they have cooled down to 3000?

 

[scubadada]

The fill pressure for Al tanks is 3000 psi, the fill pressure for HP Steel tanks is 3442 psi. At the given fill pressure they will have the rated volume. Al 80 are 77.4 cu ft, steel tanks are at their rated volume. The Aldora HP tanks, 100 or 120 cu ft, are a significant advantage for longer drift dives. This is really very simple...